1. Field of the Invention
This invention is directed to a method and apparatus for injecting implants subcutaneously in animals. More particularly, the invention relates to injecting implants, such as identification transponders, to precisely controlled distances from the point of injection. Furthermore, the injector is adjustable to be able to inject animals that range in size from small laboratory animals such as mice to large farm livestock such as cattle.
2. Description of Prior Art
Transponder, or pellet implanters, are well known. However, they have been designed for specific tasks with little or no adaptability for injection to different depths in a large variety of animals.
An early example of a pellet implanter is U.S. Pat. No. 3,744,493, issued to Boober et al. Boober et al used a simple pellet implanter having a manual plunger to force the pellets out of the end of the needle. Another simple implanter is U.S. Pat. No. 4,820,267, issued to S. M. Harmon. Harmon used a retractable cannula, or needle, and fixed plunger to force the pellets out the end of the needle when the needle is retracted. The needle is removable to load the next pellet cartridge. Also, the needle may be marked so the operator can tell the depth of implant by inserting the needle to the mark. However, holding a needle at a particular mark on the needle while injecting an animal is not practical. Unless the animal is anesthetized, it will react to the needle sting and will move during implanting. Thus, it is very difficult to hold the needle at a given insertion depth based on a mark on the needle.
One attempt to deal with the problem of controlling the depth of implant is shown in the Canadian Patent Application 2,021,303 by H. de Jong published Mar. 1, 1991. De Jong uses a transponder implanter with a touch-release button for releasing a plunger to push the transponder out of the needle as the implanter is removed from the animal. The touch-release button is at the front of the implanter at the base of the needle. Accordingly, the length that the needle extends past the touch release button controls the depth of the implant. The difficulty with de Jong's implanter is that once it is cocked and ready to fire, it is very unstable. Any contact with the touch-release button will expel the transponder from the implanter. In addition, if the animal moves while the injector is in the animal, a bump to the touch-release button will cause premature triggering of the injector while the needle is in a wrong position. Furthermore, de Jong has no way to adjust the depth of the implant.
The prior art does not solve the problem of injecting implants to a predetermined adjustable depth. Further, all of the injectors are designed to deal with animals of a particular size. The injectors are not adjustable so as to be able to inject implants in animals that vary over a wide range of sizes from farm livestock to laboratory test animals.